This invention relates to a device and method for the deionization of incoming water. Particularly, the invention is a device and method for achieving a high operating capacity through the use of the reversal of water flow in a monobed or mixed bed ion exchange deionizer, resulting in improved flow kinetics.
It is well-known in the art that deionized water can be created by moving tap water through an ion exchange resin bed. In one method, resins fill much of a cylindrical tank. The resins can be of a mixed bed type. For the purposes of this invention, a xe2x80x9cmixed bed resinxe2x80x9d is a blend of a cationic and an anionic resin, in an equivalent ratio of 1:1.
In such systems and methods, water enters the top of the cylindrical tank, and moves downwardly through the resin within the tank. When the water has moved through the resin and reached the bottom of the tank, it has been deionized (DI).
At this point, the deionized (DI) water flows into slots at the bottom of a hollow tube. The inside of the hollow tube contains no resin, but is typically surrounded by the resin within the tank. After entering the slots at the bottom of the tube, the deionized water moves upwardly through the hollow tube, and out of the tank.
High purity water can also be prepared by deionization through reverse osmosis. In high purity water systems, the ion exchange resin bed and reverse osmosis deionization technologies may be used either separately or together.
Many moderate to medium volume users of high purity water systems use ion exchange resin systems. Typically, two kinds of ion exchange resins are used for water deionization. The first kind of resin is a cationic resin, which removes cations from the water. The second kind of resin is an anionic resin, which removes anions from the water. These resins are eventually exhausted, lose their ability to deionize water, and thus need to be regenerated. These moderate to medium users of high purity water systems depend upon local service companies. In connection with such services, a tank with exhausted resin is replaced by a tank with fresh or regenerated resin. The service then regenerates the exhausted resin, using an acid such as hydrochloric acid or sulfuric acid for cationic resins, and caustic, such as sodium hydroxide, for the anionic resins. The regeneration process in such portable exchange systems takes place off site in a regeneration facility of the service provider.
There are many different versions of such prior art systems. As noted above, reverse osmosis systems may be used independently, and are viable alternatives for the preparation of high purity water. However, reverse osmosis systems are often higher in cost, require additional pretreatment and storage equipment, and typically rely upon a final, resin bed xe2x80x9cpolisherxe2x80x9d tank to provide high purity water.
Resin-based systems are also common, and are typically used where higher capacities are required. A first such resin-based system has two tanks connected in series. The first tank contains a cationic resin, and the second tank contains an anionic resin. Under such an arrangement, both such tanks are typically exhausted simultaneously. The quality of water is determined by its specific resistance; the higher the specific resistance, the higher the quality of the water. Commonly, the two tanks are removed when the specific resistance of the deionized water has fallen to about 20,000 ohms-cm.
Another resin-based system has two tanks connected in series, and both of these tanks contain a mixture of an anionic and cationic resin, otherwise known as a xe2x80x9cmixed-bedxe2x80x9d resin. This type of system, using identical tanks, provides for a main deionization tank, followed by a so-called xe2x80x9cpolisherxe2x80x9d tank. This type of system also provides for a back-up tank, in essence a second deionization tank, between the main tank and the polisher tank, to enable deionization to continue even in the event that the first tank fails or is exhausted. These types of systems are typically used where higher water purity qualities are required. The first tank is removed and replaced with a tank containing regenerated resin, when the specific resistance of the deionized water has fallen to about 200,000 ohms-cm.
A third type of resin-based system is a hybrid of the above two described resin systems. Particularly, this third system includes one tank having a cationic resin, a second tank having an anionic resin, and a third tank having a mixed bed resin. The first two tanks are the so-called xe2x80x9cworkerxe2x80x9d tanks, while the third tank is the xe2x80x9cpolisherxe2x80x9d tank, to achieve high levels of water purity.
The flow pattern on all of these prior art systems are like the prior art systems shown in FIG. 2, i.e., the xe2x80x9cdown-flowxe2x80x9d type, where the unpurified water enters the tank and moves downwardly through the resin for deionization.
The invention is a device and method for deionizing water. The first aspect of the invention comprises a device for the deionization of unpurified water. The device comprises a tank for containing a resin. The device also includes a generally hollow distributor tube in the tank for ingress into and downward movement of the unpurified water through the tank.
Slots are positioned adjacent the bottom of the generally hollow tube, and near the bottom of the tank, for distributing the unpurified water out of the hollow tube. After egress from these slots, the water moves upwardly through a bed of purifying resin within the tank. This resin in the tank surrounds the generally hollow tube, but no resin is contained within the tube. The water moves through the resin in an upward direction. After it has moved through this resin, the water is deionized.
In another aspect of the invention, the generally hollow tube is positioned substantially in the axial center of the tank. In still another aspect of the invention, the openings adjacent the bottom of the generally hollow tube are rectangular slots. In yet another aspect of the invention, the bed of ion exchange resin is a mixed bed resin.
In the method of the invention, incoming water is deionized by treatment within a tank. The method comprises placing unpurified water into the top of a generally hollow distributor tube that is positioned within the tank. This unpurified water moves downwardly through this tube.
When the incoming water reaches the bottom of the generally hollow distributor tube, it exits the tube through slots adjacent the bottom of the tube. After exiting the slots, the water is moved upwardly through a bed of ion exchange resin within the tank. In this way, the water is deionized by the resin.
In another aspect of the method, the generally hollow tube is positioned substantially in the axial center of the tank. In yet another aspect of the method, the openings adjacent the bottom of the generally hollow tube are rectangular slots. In still another aspect of the invention, the purifying resin is a mixed bed resin.
It has been found, surprisingly, that the reversal of the flow of water through the resin-containing tank both extends the operating capacity of the resin, and produces a better quality of highly purified water.
Particularly, comparing the device and process of the invention to typical down flow mixed bed ion exchange deionizers, 50-60% higher operating deionization capacity is achieved through a monobed (or mixed bed) ion exchange resin bed of the present invention""s single tank configuration. The process incorporates improved kinetics through the mixed bed ion exchange resin bed utilizing a bi-lateral flow pattern upwardly through the resin bed. The water produced is of a higher quality than water produced in most typical two bed systems. Two bed systems produce water having, on an average, 200,000-1,000,000 Ohm-cm of specific resistance. In contrast, the present invention provides water in the range of 8,000,000 Ohms at the start to 200,000 Ohms, the reverse of a typical two separate bed system. The cationic and anionic resin components are in a consistent 1:1 equivalent (40%-60% by volume) mixture. Thus, the resins are exhausted uniformly in a 1:1 ratio, providing almost neutral pH in a perfectly deionized water.
Furthermore, this process provides significant economic advantages to deionized water service companies/dealers and to the end user, because only a single tank is being used to incorporate a two bed system. Regeneration is accomplished in a single regenerator vessel. Thus, the process minimizes the amount of inventory for service tanks and resins, minimizes the cost of original regeneration capital equipment, and improves operating economics.
In a typical system design for this invention, two tanks are connected in series. The first tank is the upwardly flow high capacity deionizer, followed by a typical down flow mixed bed polisher tank. Upon exhaustion of the first xe2x80x9chigh capacityxe2x80x9d tank, the secondary tank is moved up and converted to an upwardly flow configuration, and a new polishing tank is installed. This moved up tank is found to yield an additional 50%-60% capacity in this system configuration. Only a one tank exchange is needed, thus providing customers and dealers with added economical benefits.
In contrast, in a typical two tank, separate beds system, two tanks are replaced during each exchange. These systems require an additional third polishing tank as a back up, adding to the expense of such systems.